A Powerful Window into Cosmic Evolution
Terahertz (THz) observations of interstellar atoms, molecules, and dust serve as powerful probes of the conditions within the interstellar medium that permeates our galaxy, providing insights into the origins of stars, planets, galaxies, and the Universe. Taking a cross-disciplinary approach to the subject, Terahertz Astronomy explores THz astrophysics and the technologies that make this rapidly evolving field possible.
The first four chapters of the book discuss the origin and interpretation of THz light in astrophysical sources. The remaining five chapters present an overview of the technologies used to collect and detect THz light. Every chapter contains worked-out examples and exercises. The author explains each topic as intuitively as possible and includes the equations needed for real-life astrophysical applications.
In just a few years, the number of active THz researchers has substantially grown due to increased interest in terrestrial remote sensing at THz frequencies. This book provides researchers with both the background science and technology to interpret THz observations and design, build, and deploy THz astronomical instrumentation.
Table of Contents
The Interstellar Medium at Terahertz Frequencies
ISM Components of the Milky Way
Lifecycle of the ISM
Probing the Lifecycle of the ISM
THz Radiative Transfer Basics and Line Radiation
Equation of Radiative Transfer
Solution to the Equation of Radiative Transfer under LTE (Local Thermodynamic Equilibrium)
Radiative Transfer of Rotational Transitions of Linear Molecules in LTE
THz Continuum Emission
THz Spectral Energy Distributions
Deriving Dust Optical Depth, Column Density, and Mass
Temperature and Density Distributions
Dust Energy Balance in Clouds
Dust Polarization: Origin and Measurement
Simple Radiative Transfer Model
Source Physical Conditions
Lines of Sight
Model Equation of Transfer
LTE Radiative Transfer with Hydrodynamic Simulations
Non-LTE Radiative Transfer with Hydrodynamic Simulations
THz Optical Systems
Introduction: Source-Beam Coupling
QED and Maxwell
Origin of a Single-Aperture Diffraction Pattern (QED)
Gaussian Beam Optics
Focusing Gaussian Beams
Intercepting Gaussian Beams
Illuminating THz Telescopes
THz Coherent Detection Systems
Receiver Noise Temperature
Noise Temperature of THz Optical Systems
THz Mixer Architectures and Noise
Effective Temperature Measurement of THz Components
THz Local Oscillators
Receiver Stability and Allan Time
Heterodyne Array Considerations
Background Noise Limited Operation
Instrument Noise Limited Operation
Comparing Heterodyne and Incoherent Detector Sensitivity
Incoherent Array Considerations
THz Observing Techniques
Estimating Atmospheric Optical Depth
THz Brightness Temperature of Planetary Bodies
Simple Adding Interferometer
Phase Switched Interferometer
Phasor Equation for Interferometry
Aperture Synthesis of Extended Sources
Filling-in uv Space
Transforming the Visibility Function
Map Noise Level
Phase Closure or Self-Calibration
Phase Error at THz Frequencies
Answers to Problems
Appendix 1: Timeline of Thz Technology
Appendix 2: More Thz Transitions of Atoms and Molecules
Appendix 3: Commonly Used Physical and Astronomical Quantities
Appendix 4: Useful Radiative Transfer Expressions
Appendix 5: Commonly Used Quasi-Optical Expressions
Appendix 6: Useful Heterodyne Receiver Expressions
References appear at the end of each chapter.
Christopher K. Walker is a Professor of Astronomy and an Associate Professor of Optical Sciences and Electrical & Computer Engineering at the University of Arizona. He has over 30 years of experience designing, building, and using state-of-the-art receiver systems for THz astronomy. He is the author of numerous papers on star formation and protostellar evolution, a topical editor for IEEE Transactions on TeraHertz Science and Technology, and the principal investigator of the long-duration balloon project "The Stratospheric THz Observatory (STO)" funded by NASA.
"The book is beautifully illustrated, having a long list of references and worked examples at the end of each chapter. I would recommend the book to students and researchers working in THz technologies and astronomy."
—Optics & Photonics News, January 2016
"This comprehensive, well-written book was a pleasure to read, an absolute must for anyone interested in learning about cutting-edge technologies and techniques revolutionizing our modern view of the Universe, and it is destined to become a standard reference work for astronomers and technologists."
—Professor Glenn White, The Open University
"This excellent book fills a huge hole in the literature in observational terahertz astronomy. No other existing text covers the essentials of terahertz astronomy instrumentation and techniques as applied to the study of the interstellar medium. It is sure to become an essential text for those who work in the field."
—Christopher Groppi, School of Earth and Space Exploration, Arizona State University
"… a wonderful book, combining an insightful overview of the interstellar medium with a description of the most important techniques used to study this component of galaxies and how new stars form. It’s particularly timely, with the availability of powerful new tools, including the ALMA array, the SOFIA airborne observatory, and a range of planned and proposed suborbital and space missions in the terahertz range."
—Paul F. Goldsmith, Jet Propulsion Laboratory, California Institute of Technology and Herschel Space Observatory
"This valuable and well-written textbook by Professor Christopher Walker helps to fill a gap in the literature describing the interstellar medium at terahertz frequencies. There are very few textbooks that discuss the medium from the observer’s point of view, showing how to determine its physical parameters from the output of the detectors. Also discussed are the operations of mixer and bolometer detectors."
—Thomas G. Phillips, John D. MacArthur Professor of Physics Emeritus, California Institute of Technology
"… a fundamental source for astronomers and engineers who wish to understand the physical principles and detection techniques."
—Jonathan Williams, University of Hawaii
"Walker’s book is incredibly timely: it introduces the basics of terahertz data but also explains the instrumentation at the level all observers need to know, and does so in friendly but, most importantly, crystal-clear prose."
—George H. Rieke, Regents' Professor of Astronomy, University of Arizona
"… an essential resource for all astrophysicists and experimental physicists seeking to exploit the opportunities of this last frontier in astronomy."
—Michael Burton, University of New South Wales
"The first four chapters that cover stellar evolution, atomic physics and radiation physics are the basics…. The last five are… crucial as THz data are highly dependent on the observation and calibration techniques, especially the detector technology, the improvement of which is the reason why the field has moved forward the way it is… the examples and exercises will help the readers along the way."
—Contemporary Physics (Aug 2016)